Last 3rd of LP has High Feq. Distortion

Sibilance (the "s" slurring), I presume...
Adjust yr tonearm & cartridge. Then check the cartridge loading (i.e. the input of the phono).
Only if all this fails, check/ scrap your electronics. Regards

Sounds like it could be prior mistracking of album, damage to the album. Does it do this on all lps? Otherwise, your setup is not correct.

If the problem is consistent with many records, then it's likely a setup problem.

My first question is - What is your TT/arm/cartridge?
Second question: Are you using an anti-skate adjustment?
Third: Does the problem occur if you disable anti-skate?

The reason I am honing in on anti-skate is because it varies across the record. The skating force is highest on the outer part of the record, lowest on the inner part. If you have a LOT of A/S being applied, it may be over-compensating too much on the last few tracks.

Cheers.